Polysulfone resins are well known thermoplastic materials which, due to their many advantageous properties, find use as thermoplastic engineering materials. Because of their excellent mechanical properties polysulfone resins have been proposed for various utilities including those relating to the medical field such as those relating to medical packaging, for example containers in which syringes, surgical instruments, intravenous fluids, operating room devices, and the like are stored or maintained. Additionally, the polysulfones have been proposed for medical devices such as blood oxygenators, anesthesia canisters, blood leak detectors, blood centrifuge bowls, surgical instruments and operating room instruments. The toughness of the polysulfones as well as their optical clarity, high heat resistance, strength, and physiological inertness render them suitable for use in this area of medical devices and packaging. However, in order to be used in the medical field, as well as in some other areas, sterilization of these articles is often required.
A typical method of sterilizing various articles and objects useful in the medical field is through irradiation. The type of radiation usually employed is low level gamma or electron beam radiation. It is readily apparent that the level of such radiation which accomplishes the sterilization is significantly above that of ordinary background radiation. When exposed to radiation which is of sufficient intensity and duration to sterilize various objects made from polysulfone resins the resinous material is subject to yellowing. This yellowing of the polysulfone resin reduces its clarity and alters its appearance thereby reducing its utility. Not only packaging materials such as flexible polysulfone films and sheets but also molded parts suffer from this yellowing phenomenon.
It would thus be very advantageous if polysulfone resin compositions could be provided which did not exhibit this yellowing after exposure to sterilizing irradiation. It is, therefore, an object of the instant invention to provide polysulfone compositions which exhibit improved resistance to yellowing upon exposure to sterilizing radiation.